Alkaline cells are well known in the art and generally employ a zinc anode, a manganese dioxide cathode and an aqueous solution of potassium hydroxide for the electrolyte. These cells are readily available commercially for industrial and home applications. A detrimental characteristic of these cells is the formation of hydrogen gas. The gas can be formed by undesirable electrochemical reactions which occur at the surface of the anode current collector. As the quantity of gas increases, the internal pressure in the cell also increases and if not relieved, the cells could eventually leak. In order to reduce this gas buildup, mercury may be added to the anode. Unfortunately, as is well known, mercury may add to environmental pollution when cells are eventually discarded. To replace mercury, zinc corrosion inhibitors can be added to the zinc. Examples of these inhibitors include: lead, indium, cadmium, thallium, gold, silver, tin, gallium and compounds of these elements.
A deficiency found in some of the mercury-free alkaline cells is that unexpected depression occurs in the cells' voltage during discharge. These deviations are generally temporary and the voltage generally recovers to provide the normal electrical power to the customer. This type of temporary depression and then recovery in the voltage is referred to as a "dip". The term "dud" describes a cell whose closed circuit voltage drops below an established voltage cutoff and is considered a failure. Cells plagued by temporary or permanent premature drops in the closed circuit voltage, described above as dips and duds, generally include a brass collector that was not been properly plated with zinc during the cell assembly process and/or cells in which the zinc's particle-to-particle contact is inadequate.
Another problem with some mercury-free cells is that excessive gassing can develope in cells that have been partially discharged and then allowed to rest. This situation is referred to as "post partial discharge gassing" and generally occurs when the cell utilizes a brass current collector.
Japanese Patent Application No. 61-58163 relates to an alkaline zinc battery which is an alkaline battery in which zinc is used as the anode active substance characterized in that the anode is comprised of a low amalgam of a low amalgamation ratio of less that 2% by weight or a unamalgamated zinc alloy powder and in that at least the outermost layer of the face of the anode current collector facing the anode is formed in advance by a zinc alloy of a composition that is the same as or similar to the zinc alloy powder that forms the anode.
Japanese Patent Application No. 89-307160 relates to an alkaline cell that employs a negative electrode collector body, such as brass, that is coated with a zinc alloy.
Japanese Patent Application No. 89-307, 161 relates to an alkaline cell which employs a negative electrode collector coated with indium and/or lead, and indium and/or lead substituted and deposited from aqueous solution on the surface of zinc powder as the negative electrode active material.
U.S. Pat. No. 4,939,048 relates to an electrochemical battery having an alkaline electrolyte and a gelled negative electrode containing zinc powder free from mercury, cadmium, and lead, and 1 ppm to 1000 ppm of at least one organic stabilizer compound selected from polyfluorine compounds of the ethoxyl fluoroalcohol type and compounds of the alcoyl sulfide and polyethoxyl alcohol type, the electrode being provided with a negative current collector immersed in the gell and connected to the negative terminal, wherein the current collector comprises a bundle of conducting fibers which are fixed together at their ends closest to the negative terminal, the fibers having a diameter lying in the range 0.05 mm to 1 mm, and being constituted, at least superficially, by a metal selected from: indium; gallium; cadmium; and pure zinc.
U.S. Pat. No. 4,942,101 relates to an electrochemical cell having an alkaline electrolyte and a gelled negative electrode containing zinc powder free from mercury, from cadmium, and from lead, and having 1 ppm to 1000 ppm of an organic stabilization compound selected from: polyfluoride compounds of the ethoxyl fluoroalcohol type; and compounds of the polyethoxyl alcohol and alcoyl sulfide type. The electrode is provided with a nail-shaped cylindrical negative current collector immersed in the gell and passing through a sealing plug and connected to the negative terminal. The current collector is constituted, at least superficially, by a substance selected from: pure zinc, pure cadmium, indium, and gallium; and the nail includes means assembled thereon without melting metal and serving to increase its developed surface area.
It is an object of the present invention to provide mercury-free alkaline cells that are effectively free from premature voltage depressions during discharge of the cells.
It is another object of the present invention to employ an alkaline cell with a current collector made of the same type of zinc material as the zinc material used as the anode so that unwanted voltage depressions can be effectively eliminated.
It is an object of the present invention to provide an alkaline cell with a zinc alloy anode and an anode current collector made entirely homogeneously of the same type of zinc alloy as the anode so that the amount of zinc alloy in the cell will be greater than a similar cell using a brass or other type of current collector, thus providing a greater amount of power output or capacity for the cell of the invention.
It is an object of the present invention to provide an alkaline cell with a current collector that will not form a gassing couple with the zinc alloy of the anode.
The above and further objects will become apparent upon consideration of the following description and drawings thereof.